1. Field of the Invention
The present invention relates to a fuel cell formed by stacking an electrolyte electrode assembly and a separator in a stacking direction. The electrolyte electrode assembly includes electrodes and an electrolyte interposed between the electrodes. A reactant gas supply passage and a reactant gas discharge passage extend through the fuel cell for allowing a reactant gas to flow in the stacking direction. A reactant gas flow field is formed between the electrolyte electrode assembly and the separator for allowing the reactant gas to flow along an electrode surface.
2. Description of the Related Art
The fuel cell is a system for obtaining direct current electrical energy by supplying a fuel gas (gas chiefly containing hydrogen) to an anode and supplying an oxygen-containing gas (gas chiefly containing oxygen) to a cathode for inducing electrochemical reactions at the anode and the cathode.
For example, a solid polymer electrolyte fuel cell includes a power generation cell formed by sandwiching a membrane electrode assembly between separators. The membrane electrode assembly includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane is a polymer ion exchange membrane. In use of this type of power generation cell, typically, predetermined numbers of the membrane electrode assemblies and the separators are stacked together to form a fuel cell stack of the power generation cells, e.g., mounted in a vehicle.
In the fuel cell, a fuel gas flow field (reactant gas flow field) for supplying a fuel gas is formed on a separator surface facing the anode, and an oxygen-containing gas flow field (reactant gas flow field) for supplying an oxygen-containing gas is formed on a separator surface facing the cathode.
Further, so-called internal manifold structure may be adopted in the fuel cell. In the structure, an oxygen-containing gas supply passage and an oxygen-containing gas discharge passage extend through the fuel cell for allowing an oxygen-containing gas to flow through the fuel cell in the stacking direction, and a fuel gas supply passage and a fuel gas discharge passage extend through the fuel cell for allowing a fuel gas to flow through the fuel cell in the stacking direction. Further, a coolant supply passage and a coolant discharge passage extend through the fuel cell for allowing a coolant to flow through the fuel cell in the stacking direction.
In the reactant gas flow fields, condensed water is produced, and water produced in the power generation is present. The water tends to be retained at the outlet of the reactant gas flow fields. In the structure, the reactant gas flow fields may be clogged by the retained water, and the fuel gas and the oxygen-containing gas may not be supplied to the anode and the cathode suitably.
In this regard, for example, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2000-223137 includes a separator 1 as shown in FIG. 9. A fuel gas inlet 2a, an air inlet 3a, a coolant inlet 4a are arranged diagonally with a fuel gas outlet 2b, an air outlet 3b, and a coolant outlet 4b in the separator 1, and the inlets and the outlets extend through the separator 1.
An air channel 5 having a plurality of air flow grooves 5a are formed on one surface of the separator 1 for allowing the air supplied from the air inlet 3a to flow toward the air outlet 3b. The air flow grooves 5a of the air channel 5 flow in parallel, and form a serpentine flow field for allowing the air to flow left and right, and move downwardly.
The air flow grooves 5a of the air channel 5 are configured such that the sectional area in the flow field is progressively reduced from the air inlet 3a to the air outlet 3b, i.e., toward the downstream side. According to the disclosure, reduction in the flow speed at the air outlet 3b is suppressed, and the water is not retained easily on the air outlet 3b side advantageously.
However, in Japanese Laid-Open Patent Publication No. 2000-223137, since the air flow grooves 5a form the serpentine flow field, the flow grooves connecting the air inlet 3a to the air outlet 3b are significantly long. In the structure, the pressure loss in each of the air flow grooves 5a is significantly large. In particular, it is required to keep the high outputs of devices such as a compressor and a supercharger for supplying the air to the air inlet 3a. Therefore, the devices have large sizes uneconomically.
Further, in a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-032008, as shown in FIG. 10, a hydrogen side separator 1c is provided. The separator 1c is formed by a single metal plate 2c. The separator 1c has a corrugated power generation area 3c formed by pressure forming.
A hydrogen gas flow field 4c is formed on one surface of the separator 1c, and a coolant water flow field is formed on the other surface of the separator 1c. A hydrogen gas distribution channel 5c for distributing a hydrogen gas to the hydrogen gas flow field 4c is formed inside a rib 6c formed integrally with the metal plate 2c by resin molding. A hydrogen manifold hole 7c, a coolant water manifold hole 8c, and an air manifold hole 9c extend through the separator 1c in the stacking direction. The hydrogen manifold hole 7c is connected to the hydrogen gas flow field 4c through the hydrogen gas distribution channel 5c. 
However, in Japanese Laid-Open Patent Publication No. 2006-032008, the hydrogen cannot be distributed uniformly from the hydrogen manifold hole 7c to the hydrogen gas flow field 4c easily, and the hydrogen distribution performance is low. By designing flow grooves in the hydrogen gas distribution channel 5c connecting the hydrogen manifold hole 7c to the hydrogen gas flow field 4c to be considerably long, the desired hydrogen distribution performance may be achieved. However, in the structure, the separator 1 itself has a large size in the flow direction of the hydrogen gas flow field 4c, adversely.